With the spread of information terminals, there are increasing demands for a flat panel display that serves as a display for a computer. Further, with development of the information technology, there has been increased a chance for information offered in a form of a sheet of paper medium in the past to be offered in an electronic form. An electronic paper or a digital paper is demanded increasingly as a display medium for a mobile that is thin, lightweight and handy.
In the case of a display device of a flat sheet type, a display medium is generally formed using an element that employs a liquid crystal, organic EL or electrophoresis method. In the display medium of this kind, a technology for using an active driving element comprised of a thin-film transistor (TFT), serving as an image driving element, is the main current for ensuring uniform image brightness and an image rewriting speed.
The TFT is manufactured by a process comprising forming, on a glass substrate, a semiconductor layer of a-Si (amorphous silicone) or p-Si (poly-silicone) and metal films of source, drain and gate electrodes, in the order. In the manufacture of a flat panel display employing such a TFT, a photolithography step with high precision is required in addition to a thin layer forming step requiring a vacuum line carrying out a CVD method or a sputtering method or a high temperature treatment step, which,results in great increase of manufacturing cost or running cost. Recent demand for a large-sized display panel further increases those costs described above.
In order to overcome the above-described defects, an organic thin-film transistor employing an organic semiconducting material has been extensively studied (refer to Japanese Patent O.P.I. Publication No. 10-19000 and “Advanced Material”, 2002, No. 2, p. 99 (review)). Since the organic thin-film transistor can be manufactured at low temperature employing a lightweight substrate difficult to be broken, a flexible display employing a resin film as a substrate can be realized (refer to SID '02 Digest P. 57). Further, employing an organic semiconducting material allowing a wet process such as a printing method or a coating method, a display manufacturing process can be realized which provides excellent productivity and reduced cost.
However, an organic thin-film transistor, when allowed to stand in air, deteriorates, resulting in lowering of transistor properties. Further, an organic thin-film transistor, when manufactured by a process comprising forming an organic semiconductor layer, followed by coating of a light sensitive resin layer, and development of the light sensitive resin layer air, results in deterioration of transistor properties due to a solvent used for coating or components contained in a developer used for development.
An organic thin-film transistor employing a substrate such as a resin plate or a resin film is easily folded as compared with that employing a glass plate. Therefore, the former has problem in that properties as a transistor deteriorate due to folding, or due to light.